You can build strength pretty effectively, especially with someone wo's de conditioned. With once or twice a week. In fact, there was a study that just came out that showed that ive minutes swere to god, five minutes of isometric exercise. So they had adults who were deconditioned do flexing poses five minutes a day, pushing against an immovable object for five minutes. They saw significant strength and muscle gains. Now, at some point that'll stop because your body will adapt, and th you'll need a little more. But that just goes to show you don't need a lot.